Groundwater aquifers are a main source of drinking water for billions of people worldwide. There is, however, growing public concern about chronic exposure to natural, geogenic contaminants that can be released from uncontaminated sediment to groundwater. Natural constituents of groundwater recognized to be of significant health concern include fluoride and manganese. The metalloid arsenic (As) has received attention as a contaminant over the past two decades, particularly in south and southeast Asia. For example, elevated groundwater arsenic concentrations in many parts of Bangladesh has been described as the “largest poisoning of a population in history.” Estimates of the rural population exposed to unsafe arsenic levels by drinking water in India, China, Myanmar, Pakistan Vietnam, Nepal and Cambodia has grown to over 100 million people.
Inappropriate sampling is one reason the multiple biogeochemical and hydrological factors contributing to the release of arsenic and other contaminants to groundwater have been difficult to isolate and fully understand, despite two decades of research by numerous international teams. Groundwater and aquifer solids are often collected separately by installing a well and coring to approximately the same depth, respectively. The high spatial variability within floodplain and delta deposits makes it therefore difficult to properly match solid phase and groundwater characteristics. Combining groundwater and sediment for incubation experiments can also create artifacts because of exposure of originally anoxic groundwater to atmospheric oxygen, contamination of the sediment with drilling fluid, and changing the in situ water/rock ratio. The mechanism of release and transport in groundwater of arsenic and other geogenic contaminants can hamper the ability to predict the fate of aquifer zones that can yield groundwater safe for human consumption. Nevertheless, such groundwater holds the greatest promise for reducing human exposure to natural contaminants in south and southeast Asia and other parts of the world in the foreseeable future.
Core catchers have been developed that attempt to minimize the loss of sediment upon retrieval, such devices can still result in the loss of sediment (e.g., sand) upon retrieval. Even when effective, core catchers also do not retain groundwater originally in contact with the sampled sediment interval.
Another approach to groundwater sample recovery is to seal the end of the coring tube, before retrieval, by freezing the contents with liquid CO2 or N2. See Murphy et al., A Sample-freezing Drive Shoe for a Wire Line Piston Core Sampler, Groundwater Monitoring Review, 16:86-90 (1996), which is hereby incorporated by reference. This approach can require a drill rig, sampling processing labs and liquid CO2 or N2 on hand at the field location.
Thus there remains a need for an efficient groundwater sampling tool to collect and process uncompromised aquifer samples, containing both sediment and groundwater, that can be easily implemented in the field and that does not require refrigerants like CO2 or N2. Such a tool would be useful for documenting and studying both natural and anthropogenic contamination of groundwater.